Study Of The Influences Of N-nitrosamine Inhibitors And Other Factors On Properties And N-nitrosamine Content Of Natural Rubber Latex Film

Natural rubber latex products are widely used in industry, agriculture, health care and other areas. At present, secondary amine type vulcanization accelerators (such as zinc diethyl dithiocarbamate ZDC, tetramethyl thiuram disulfide TMTD, et al.) are often used in the production process of natural rubber latex products, which are easy to produce carcinogenic N-nitrosamine in curing process. It is a serious threat to people’s health. Therefore, reducing the content of N-nitrosamine is one of the biggest problems of the natural rubber latex product industry needed to solve. In this study, the sulfur vulcanization system was used. The influences of the species and amounts of alkaline earth metal hydroxides (Ca(OH)2(calcium hydroxide), Ba(OH)2(barium hydroxide), et al.), ascorbic acid, a-tocopherol on the content of N-nitrosamine of vulcanized natural rubber latex films with ZDC as vulcanization accelerator were investigated. And the influences of the front factors on the curing characteristics and colloid properties of natural latex, as well as mechanical properties of vulcanized natural rubber latex films were also investigated. The influences of varying process conditions including curing temperature and leaching on the content of N-nitrosamine of vulcanized natural rubber latex films prepared separately with zinc diisobutyl dithiocarbamate (ZDiBC) and ZDC as vulcanization accelerator were investigated. Effects of different sulfur vulcanization systems on the mechanical properties of vulcanized natural rubber latex films prepared with environmental accelerator ZDiBC used were investigated. In addition, orthogonal design experiment was used with S+ZDiBC+ZnO as the curing system to investigate the influences of S(sulfur), ZDiBC and ZnO(zinc oxide) on mechanical properties of vulcanized natural rubber latex films.The results showed that:Ca(OH)2, Ba(OH)2and Mg(OH)2(magnesium hydroxide) can significantly reduce the content of N-nitrosamine of vulcanized natural rubber latex films, in which Ba(OH)2was the most significant, and with the dosage increasing, the extent of reducing can be up to97.56%; ascorbic acid(VC) and a-tocopherol(VE) can reduce the content of N-nitrosamine of vulcanized natural rubber latex films, and the content of N-nitrosamine can be reduced to<0.01mg/kg with VC; leaching can reduce the content of N-nitrosamine; the influences of environmental accelerator (zinc diisobutyl dithiocarbamate ZDiBC) and conventional accelerator (zinc diethyl dithiocarbamate ZDC) on the content of N-nitrosamine of vulcanized natural rubber latex films were different, with the improving of curing temperature, the content of N-nitrosamine of vulcanized natural rubber latex film with ZDC reduced, while that with ZDiBC increased. Ca(OH)2, Ba(OH)2and Mg(OH)2may affect the viscosity and mechanical stability during storage of natural rubber latex, in which Ca(OH)2had the greatest impact on the viscosity, while Ba(OH)2had the greatest impact on the mechanical stability. Ca(OH)2, Ba(OH)2and Mg(OH)2could make the curing time reduce gradually with the amount increasing. With the amount of Ca(OH)2increasing from0.0phr to0.9phr, the tensile strength, tear strength, modulus and crosslink density of vulcanized natural rubber latex films gradually improved. With the amount of Ba(OH)2and Mg(OH)2increasing from0.0phr to0.9phr, tensile strength, tear strength, modulus and crosslink density of vulcanized latex films showed a decreasing trend after the first increase.Ascorbic acid could reduce the mechanical stability degree and increase the viscosity of natural rubber latex. Ascorbic acid (VC) and a-tocopherol (VE) caused an extension of curing time of the natural rubber latex film. With the increase in the amount of VC (0.0-0.9phr), the tensile strength, tear strength, modulus and crosslink density of the vulcanized film decreased gradually. With the increase in the amount of VE (0.0-0.9phr), the modulus, tensile strength, tear strength, and crosslink density of the vulcanized film decreased firstly, and then increased gradually.Different sulfur vulcanization systems had different effects on the mechanical properties of vulcanized natural rubber latex films. Whether vulcanized latex films prepared by unvulcanized latex, or vulcanized latex films made by unvulcanized latex, the mechanical properties of them are both the best in general sulfur vulcanization system (CV).Orthogonal test showed that:in the curing system of S+ZDiBC+ZnO, the influences of ZDiBC, S, ZnO on each performance indicator of vulcanized natural rubber latex film were different. Sulfur had a maximum impact on the tensile strength,300%modulus and crosslink density.